[cobrajam]

I would start with the pinion angle. I experienced this with my Midstates the first time out too. Some info says to align the pinion angle the same as the transmission yoke angle. Throw that out, try to 'point' the pinion down, that is if you have Midstates four link. This is accomplished by extending the lower links and/or shortening the upper links. If your tires are currently where you want them in the wheelwells, you will need to adjust both a little.
Do it in small increments, may take you 3-4 times to reach the 'sweet' spot. If memory serves me, my pinion needed to be pointed down just under level.